Fungus and columnaris
White fluffy or cotton-like patches.
White to gray cotton-wool tufts on the skin, fins or mouth, or a pale saddle-shaped patch on the back. Fungus usually grows on an existing wound; columnaris is a fast bacterial infection that can kill within days.
- Do this first
- Move the fish to a hospital tank if you can; test and change the water in the main tank.
- Call a vet when
- Call a fish vet the same day if patches spread, appear on the mouth or gills, or more than one fish is affected.
Likely causes
- Injuries and torn fins
- Poor water quality and high temperature (columnaris)
- Stress after transport
What to do today
- Move the fish to a hospital tank if you can; test and change the water in the main tank.
- Remove any dead fish at once.
- Columnaris spreads quickly: if patches appear on several fish or around mouths, get advice the same day.
When to call a vet
Call a fish vet the same day if patches spread, appear on the mouth or gills, or more than one fish is affected. A vet who treats fish can examine it and prescribe treatment; your local fish store or aquarium society can often recommend one.
Stop it happening again
Handle fish gently, keep water clean and quarantine new arrivals. How to set up a quarantine tank.
Sources: Merck Veterinary Manual: Management of aquarium fish; Merck Veterinary Manual: Disorders and diseases of fish; UF/IFAS: Ammonia in Aquatic Systems.